package codeRandomThoughts.Test115不同的子序列;

public class Solution3 {
    public int numDistinct(String s, String t) {
        //dp[i][j]:以t[j-1]为结尾的字符串在以s[i-1]为结尾的字符串中出现的次数
        int[][] dp = new int[s.length() + 1][t.length() + 1];

        //空集是所有字符串的子集
        for (int i = 0; i <= s.length(); i++) {
            dp[i][0] = 1;
        }

        for (int i = 1; i <= s.length(); i++) {
            for (int j = 1; j <= t.length(); j++) {
                if (s.charAt(i - 1) == t.charAt(j - 1)) {
                    dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j];
                } else {
                    dp[i][j] = dp[i - 1][j];
                }
            }
        }

        return dp[s.length()][t.length()];
    }
}
